This invention relates to a separable fixture for applying a compressive load to anisotropic conductive elastomer material in an electrical connector.
A compliant interposer connector (a sheet of anisotropic conductive elastomer (ACE) material) is compressed as part of a separable electrical connector between an electrical device and a corresponding array of electrically conductive pads on a substrate (e.g. a printed circuit board). The interposer conducts electricity vertically between each pad on the device and the corresponding pad on the substrate, while electrically isolating the pads from their laterally-adjacent neighbors. This has been done using a spring preload to compress the ACE between the device and the substrate.
One method of spring preloading such a system has been to have a flat, rigid backup plate below the substrate with four pins or bolts going up through four corresponding holes in the substrate. The interposer connector sits on pads on the top surface of the substrate; the device sits on the interposer connector; and a rigid plate, typically a heat sink, sits on the device. The four pins passing through the substrate typically go through clearance holes in the interposer connector, and extend upwards past the device through holes or slots in the heat sink. Above the heat sink, lock washers and nuts are placed on the ends of the pins. Tightening these nuts pulls the heat sink down, compressing the substrate/interposer connector/device stack-up between the backup plate and the heat sink. The advantage of this system is that the device can be replaced without accessing any hardware below the substrate. The disadvantage of this system is that the forces on the four pins must be carefully balanced to compress the system evenly.
Another disadvantage of this system is that the compressive spring element is the interposer itself which, in general, has poor spring characteristics. In one modification of the above described system, coil springs are placed over each of the four posts, between the heat sink and the washer/nut assembly. The springs can be designed to assure a quality compressive load. The problem of carefully tightening the springs to assure a balanced load remains a disadvantage of this design.
Another method of spring preloading the system has been to have four pins or bolts dropping down from the heat sink, through clearance holes in the interposer connector, the substrate, and a flat rigid backup plate. Holes or slots in a spring plate located below the rigid backup plate engage the four pins. The center of the spring plate has a threaded insert. The system is compressed using a set screw passing through the spring plate and engaged in the threaded insert by forcing the set screw against the backup plate, thus flexing the spring plate and compressing the substrate/interposer connector/device stack-up between the backup plate and the heat sink. The advantage of this system is that the forces on the stack-up are intrinsically centered since the only load applied to the backup plate is applied at its center. The disadvantage of this system is that the device cannot be replaced without accessing both the device side of the substrate and the set screw in the spring plate on the opposite side of the substrate. In many instances, access to the bottom of the board is not available.
It is therefore an object of this invention to provide an apparatus for applying a mechanically-releasable balanced compressive load to a compliant anisotropic conductive elastomer (ACE) electrical connector.
It is a further object of this invention to provide such an apparatus that can be operated in situations in which there is access to only one side of the substrate (printed circuit board).
This invention features an apparatus for applying a mechanically-releasable balanced compressive load to a compliant anisotropic conductive elastomer (ACE) electrical connector that electrically connects an electrical device to a first side of a two-sided substrate. In one embodiment, the apparatus comprises a backup plate against the second side of the substrate, and a rocker plate against the backup plate, the rocker plate touching the backup plate only at the center of the backup plate. There is also a rigid member on the electrical device, and a plurality of pins mechanically coupled to the rocker plate and the rigid member. At least one spring member is mechanically coupled to at least one pin, for applying a variable force coupled through the at least one pin to the rocker plate, to urge the backup plate and rigid member together and thereby compress the ACE between the electrical device and the substrate.
The apparatus may further comprise means for varying the force applied by at least one spring member to at least one pin. The spring member may comprise a coil spring, a washer or disc spring (Belleville washer) or a flexible plate, for example. The apparatus may comprise two spaced flexible plates that are the springs. The apparatus may comprise four pins, and the pins may be spaced equally from the center of the backup plate. Each of the pins may be coupled to the rigid member through a flexible plate, with two of the pins coupled to spaced locations of one plate, and the other two pins coupled to spaced locations of the other plate. The means for varying the force may then comprise means for controlling the amount of flex of at least one plate. The means for controlling the amount of flex may comprise a cam arrangement for variably displacing the plate relative to the rigid member.
The apparatus may further comprise means for releasably engaging each pin with a plate. The means for releasably engaging may comprise a slot in the plate having a wider portion and a more narrow portion, to engage and disengage a pin. The pins may include an enlarged head that is smaller than the wider portion of the slot and larger than the more narrow portion of the slot, so that the pin can be releasably retained in the slot. The plates may each be laterally movable to engage and disengage the enlarged heads of the pins, to allow the rigid member to be removed from the device.
The apparatus may further comprise a rocker arm mechanically coupled to two pins and in contact with the rocker plate at a single, central pivot. The pivot point may be equally spaced from the two pins to which the rocker arm is coupled. The spring member may be coupled to a pin and to the rocker plate. The spring member may be coupled to a pin and to the rigid member.
The backup plate may have diagonally opposite corners, and the spring member may comprise a spring rocker plate coupled to pins proximate the diagonally opposite corners. The spring rocker plate may span a plurality of backup plates, each with diagonally opposite corners, and the spring rocker plate may be coupled to pins proximate the diagonally opposite corners of each backup plate. A set screw engaged in the rocker plate may accomplish the touch of the rocker plate to the backup plate. The set screw may be threaded in the rocker plate, so that the length of the set screw between the rocker plate and the backup plate can be varied.
Also featured is an apparatus for applying a mechanically-releasable balanced compressive load to a compliant anisotropic conductive elastomer (ACE) electrical connector that electrically connects an electrical device to a first side of a two-sided substrate, comprising a backup plate against the second side of the substrate, a rocker plate against the backup plate, the rocker plate touching the backup plate only at the center of the backup plate, and a rigid member on the electrical device. Also included are a plurality of pins mechanically coupled to the rocker plate and the rigid member, and at least one spring member mechanically coupled to at least one pin, for applying a variable force coupled through the at least one pin to the rocker plate, to urge the backup plate and rigid member together and thereby compress the ACE between the electrical device and the substrate. This embodiment further includes means for varying the force applied by at least one spring member to at least one pin, wherein a set screw threaded in the rocker plate accomplishes the touch of the rocker plate to the backup plate, so that the length of the set screw between the rocker plate and the backup plate can be varied. The invention can be used in a number of additional applications in which a uniform clamping load is needed. Some of the examples envisioned include:
1. Quick release clamping of photo plates. In this example a thick glass plate with holes in the four corners would be clamped so as to uniformly load a film to the exposed element (film or photo resist on a printed circuit board etc.)
2. Clamping of biological samples. A microscope stage could incorporate the inventive clamping system to hold samples in the optical plane.
3. Quick release gluing fixture. When gluing sheet materials, the invention can accomplish a quick release clamp that provides a uniform load between sheets being glued.
4. Uniform loading gasket system. When mounting gaskets it is critically important to uniformly tighten the load around the gasket to have a good seal. This is a common problem in automobile head gaskets, vacuum systems etc. The invention could be employed to generate a uniform load on the entire structure while tightening a single bolt.
5. Tool machining fixture. The clamping of thin materials for machining operations is always a challenge. The invention could provide a quick release uniform loading clamp.